Introduction to C# 3

Introduction

Just look at the C# 3 future, it's so pretty I want it now. Check out the videos that they have there. There is so much good stuff there, and it's only the start. First of all, read the C# 3.0 spec [doc file], or just read the rest of the post to see the highlights.

Type Inferencing and Implicitly Typed Arrays

I got addicted to that when using Boo, it's something so simple, but it saves so much. In most cases, it means no more casting hell. Andres let it slip in a presentation about a year ago, in essence, it means:

This is a very cool idea, especially since you can use it for the foreach construct, which should make for far better code. Did you notice how I declared the array? new [], without a type, the compiler just fixed it up automatically.

Extensions Methods

This is a feature that lets you add new instance methods to a class, without touching the class code and even if the class is already compiled. The idea opens up so many possibilities that it's just staggering. Fowler talked about it in Refactoring. Other languages, such as SmallTalk and Ruby already have it (SmallTalk has it for 30 years, I think), and it has proved to be a useful feature. You could add methods to System.Object, which would then be "inherited" by any object. Consider adding ToXmlString() for all objects, for instance. Or persistence to database. And no, it's not just syntactic sugar, those things are important. This mean that you're no longer at the mercy of the class designer. It's a truly powerful tool. The nicest thing about it, I think, is that it'll work with generics, so you get a host of goodness for very little effort. Here is the example from the spec:

What does the above say? Well, it means that you can now use Select() on any object that implements IEnumerable. You could even use them on your 1.0 and1.1 collections! Can you say goodness? This is cool on so many levels that it's not even funny.

Extension properties, events and operators are currently considered, but not yet supported. I certainly hope that Microsoft will implement those, as they would allow a much nicer syntax for a lot of things (an IsNull property, for a start). Adding operators to interfaces is another big problem that this can solve.

Lambda Expressions

This is like anonymous methods, only with an even easier syntax. This is something that I don't think most .NET developers will appreciate now, but they certainly would two years from now, when the functional goodness will be fully entranced. Here is how you would extract all the names from a list of customers:

string[] names = GetListOfCustomers().Select( c => c.Name );

Can you see the beauty of it? The "c => c.Name" is the lambda expression, which is just a way to tell the compiler to do the dirty work, instead of having to do it ourselves using anonymous delegates. If it was all that they were good for, they wouldn't amount to much, but they have quite a few other usages, as you'll see shortly.

Object and Collection Initializers

This is something that we had for quite some time in attributes, which is now coming to both object initialization and collections initialization. The idea is actually very simple, consider the class Person:

This would create a new type with Name and WebSite properties. While this may save some typing in certain cases, I'm not certain that this is a useful feature. You cannot use it outside of a method's boundary, since it has no type that you can access.

This is nice, but I don't like the way it's implemented now. Boo has something similar, but since Boo has type inferencing throughout the language there it actually makes sense, since it allows to return a strongly typed object from a method, instead of an object array. Here is the Boo example:

Since declaring variables using the var syntax is limited to local variables, I think this is unnecessarily limited.

Query Expressions

I expect this to be the big thing for C# 3, just as generics are the big thing for C# 2. The idea is to allow an SQL like syntax for selecting objects from a database/memory/XML directly into the language. The idea is quite involved, and I'm sure it will generate a lot of discussion. The idea is to be able to do the following:

There are all sorts of ways where you can plug into this statement and do all sorts of cool things with it. db.Customers may be an in memory class, or it can redirect the query to database, to remote machine, etc. This is also apparently the use case for anonymous types, as return types from lambda expressions. It's nice, but it's not enough. It should be expanded to regular methods as well, in my opinion. I suggest checking the spec anyway, I'm just touching the edge here, and I'm sure that there are a lot of cool implementations that I'm missing here.

Expression Trees

They are a way to turn lambda expressions into data. The idea is to be able to do this:

var valuedCustomers = session.Select(x => x.IsValued==true);

What is this? Well, what happened here is that we saved the lambda expression "x => x.IsValued==true" and passed it to a persistence layer, which would parse the expression, and load from the database all the rows for which the expression is true.

The important thing here is that the Select method is not using a opaque string, but code that can be type checked and verified by the compiler. Presumably refactoring tools for C# 3 will also support this, so it will make life even easier.

For the author of the Select() method, life would be much easier as well. He won't have to parse strings, but rather deal with an AST tree. From experience, I know that dealing with ASTs is not the easiest thing in the world, but it's certainly much better than dealing with strings.

Summary

All in all, I really like the direction that C# 3 is heading for. Functional programming is not appropriate all the time, but it can save quite a bit of typing and a lot of awkward syntax. I'm very excited about the new abilities, and I think that they will present a quantum leap much bigger than 1.1 -> 2.0. Considering that those are just the language enhancements, I can hardly grasp the amount of goodness we will get in the class library and the associated tools.

I expect quite a lot of noise about query expressions (yes, they are cool). And a lot of activity in the area of lambda expressions as data, since it's a cool way to express much more than just ORM syntax.